While plotters have been used heretofore to write a variety of images, such plotters have been adapted for use only with ball point or felt tip pens, pens which are not suitable for performing calligraphic writing. Notwithstanding the clear advantages in having calligraphic writing done automatically, particularly in tedious applications such as addressing invitation envelopes, there are a number of problems which have prevented calligraphic pens, such as calligraphic fountain pens or spring-loaded plastic-tip marker pens, from being used in conventional plotters. One of the most serious of these problems is maintaining flow of ink or other writing fluid in the pen, particularly during short intervals when the pen is not writing, and assuring that ink is flowing properly before a large number of envelopes or other documents are ruined.
There are a number of ways in which ink flow may be interrupted in a calligraphic pen. First, most inks used in the pens, particularly the colored inks, consist of pigment particles suspended in a liquid solution. If the pen, and the ink therein, is not continuously, or at least periodically, agitated, the pigment particles will migrate under the force of gravity to the bottom of the pen's ink reservoir and will solidify, blocking ink flow. With spring-loaded plastic-tip marker pens, ink flows when the point is pressed against the paper or other writing surface as on a downstroke of the pen. If ink is not maintained flowing, the ink can dry out resulting in poor quality writing. This can occur when the pen is idle or during long periods of continuous writing. Similarly, when a fountain pen is not in use, residual ink in the channel or grove of the pen nib can dry up and solidify, blocking the channel and preventing ink flow the next time an attempt is made to use the pen.